This relates generally to image sensors and, more particularly, to electron multiplying charge coupled device (EMCCD) image sensors.
Modern electronic devices such as cellular telephones, cameras, and computers often use digital image sensors. Image sensors (sometimes referred to as imagers) may be formed from a two-dimensional array of image sensing pixels. Each pixel includes a photosensitive region that receives incident photons (light) and converts the photons into electrical signals. Image sensors are sometimes designed to provide images to electronic devices using a Joint Photographic Experts Group (JPEG) format.
Conventional image pixel arrays may be fabricated on a semiconductor substrate using complementary metal-oxide-semiconductor (CMOS) technology or charge-coupled device (CCD) technology. Certain CCD image sensors, referred to as electronic multiplying charge coupled device (EMCCD) image sensors, have high sensitivity and multiply collected charge in the charge domain using a single carrier impact ionization process before charge is converted into a voltage at the CCD charge detection output node. However, EMCCD image sensors may experience a gain ageing effect where trapped electron charge builds up during the device operation lifetime. The trapped electron charge causes a significant potential shift in the silicon under the charge multiplication gate, which reduces the charge multiplication gain.
It would therefore be desirable to be able to provide improved EMCCDs with stable charge multiplication gain.